The present invention relates to an ion beam device and ion beam processing method for carrying out section processing by irradiating an ion beam to a specified part of a sample, and also to a holder member for fixing the sample.
As an ion beam device, a focused ion beam device and an ion milling device are known. These devices are used in sample manufacture when carrying out section observation of fault locations of a wafer using a TEM (Transmission Electron Microscope), for example. In particular, since an FIB device scans a sample surface with a sufficiently focused ion beam and can perform accurate section processing of specific sites such as defects while detecting secondary electrons generated at the time of scanning and observing as an image, FIB devices are widely used as evaluation devices for semiconductor manufacturing processes. Recently, combination type ion beam devices that combine FIB devices and observation devices such as scanning electron microscopes or energy dispersive X-ray detectors, have also been proposed.
The schematic structure of a conventional FIB device is shown in FIG. 8. The main parts of this FIB device are an ion source 100, an ion optical system 101, a secondary charged particle detector 102, a gas gun 103, a sample holder 104 and a sample stage 105.
The ion source 100 is a liquid metal ion source exemplified by Gallium (Ga), for example. The ion optical system 101 is for focusing an ion beam from the ion source 100, as well as scanning the ion beam on the sample 106, and has a condenser lens (electrostatic lens), beam blanker, movable aperture, 8-pole stigmeter, objective lens (electrostatic lens) and scanning electrodes arranged in order from the ion source 100. The secondary charged particle detector 102 detects secondary charge particles generated when the focused ion beam (hereafter referred to simply as FIB) scans the sample 106.
The sample stage 105 can be controlled along five axes. With five axes of control, it is possible to control three dimensional movement in the XYZ directions, rotation around an axis perpendicular to the XY plane, and tilt. The sample holder 104 is for fixing the sample 106, and the sample is conveyed on the sample holder 104 mounted on a moving platform called a boat (not shown in the drawings). The sample 106 is a chip sample subjected to preliminary processing by cutting, for example, defect locations from a wafer using a dicing saw.
One example of a method of fixing the sample 106 to the sample holder 104 is shown in FIG. 9(a) to FIG. 9(b). A discoid sample holding member 110 that has had a substantially E-shaped part cut out (generally called a mesh) as shown in FIG. 9(a) is prepared, and a step section 112 as shown in FIG. 9(b) is formed by bending a middle part 111 of this sample holding member 110 so as to be substantially perpendicular to the disc surface. Next, as shown in FIG. 9(c), a sample 106 that has been processed into a substantially rectangular block using a dicing saw is mounted on a side surface formed by the step section 112 of the sample holding member 110. At this time, one end surface of the longer edge sides of the sample 106 is in contact with the step section 112. In this state, both ends of the shorter edges of the sample 106 are fixed to the sample holding member 110 using adhesive 113.
The sample holder 104 comprises a clamp section made up of a receiving section 104a and a press contact section 104b, as shown in FIG. 9(d), and a fixing platform (not shown) to which the clamp section is fixed. A part of the sample holding member 110 that is opposite to a part to which the sample 106 is fixed is clamped by being sandwiched by the receive section 104a and the press contact section 104b. At the time of clamping, by bringing the step section 112 into contact with the upper surface of the press contact section 104b, a clamp position of the sample holding member 110 is regulated. In this manner, the clamp section is fixed to the fixing platform with the sample holding member 110 clamped.
Clamping of the clamp section to the fixing table is carried out by engaging projections (not shown) provided at specified places of the fixing platform into holes 104c respectively provided on both ends of the receiving section 104a, for example. Alternatively, it is also possible for fixing of the clamp section to the fixing platform to have a detachable structure using a latch mechanism.
The sample holder 104 is mounted on a moving table (not shown), and conveyed to the sample stage 105. The fixing platform for the sample holder 104 can also serve as the moving table.
Next, a description will be given of the basic sample manufacturing sequence that uses the above described FIB device. FIG. 10(a) to FIG. 10(c) are process drawings showing a manufacturing sequence for a TEM sample. In the following, the manufacturing sequence for a TEM sample will be described with reference to FIG. 8-FIG. 10.
A defect location of a wafer is subjected to preliminary processing by cutting with a dicing saw, and a convex-shaped sample 200 having a cross section as shown in FIG. 10(a) is formed. The surface of the projecting section of the sample 200 is the surface of the wafer, and in subsequent description the surface of this projection will be made the surface of the sample, while the opposite surface will be made the rear surface of the sample. This sample 200 is clamped to the sample holder 104 by fastening to a sample holder member 110 shown in FIG. 9(d) in a state where the rear surface is in contact with the step section 112. Then, the sample holder 104 is mounted on the moving table (not shown) and conveyed onto the sample stage 105, and position and angle are adjusted on the sample stage 105 so that an FIB from the ion source 100 is irradiated substantially perpendicular to the surface of the sample 200.
Next, specified gas is sprayed onto the surface of the sample 200 using a gas gun 103, and by scanning a range including a region of the surface of the sample 200 to be processed using the FIB from the ion source 100 a protective film 201 as shown in FIG. 10(b) is formed.
Finally, the process region of the surface of the sample 200 is scanned by the FIB from the ion source 100. Since the FIB is irradiated so as to be substantially perpendicular to the surface of the sample 200, the region where the FIB is irradiated has a surface that is gradually shaved off, and finally the cross section 202 shown in FIG. 10(c) is obtained. The cross section 202 shown in FIG. 10(c) is the projection section of the sample 200 shaved away from both sides, and the thickness is from 0.1 to 0.5 μm. The cross section 202 formed in this way is used as TEM sample.
With the above described slicing process, there is damage to the cross section 202 by the FIB. FIG. 11(a) is a perspective view of the TEM sample made with the sequence of FIG. 10(a) to FIG. 10(c) using a Ga ion source as the ion source, and FIG. 11(b) is a cross sectional drawing along line A-A′ in FIG. 11(a). In the case of carrying out slicing processing using the FIB from the Ga ion source, the surface of the cross section 202 is subjected to damage by the FIB, and also some of the Ga ions contained in the FIB are injected, to form the damage layer (fracture layer) 203 as shown in FIG. 11(b). The damage layer 203 has an amorphous state with a mixture of elements originally included in the sample itself and injected Ga. If the unwanted damage layer 203 is formed on the surface to be observed in this way, the damage layer proves a hindrance and it is not possible to carry out TEM observation in a satisfactory manner.
A method of removing the damage layer by etching (ion milling) using a low energy ion beam, for example, an argon (Ar) ion beam has been proposed. For example, in Japanese Patent publication No. 3117836 (Japanese Patent Laid-open No. Hei.6-260129), there is disclosed an FIB device capable of removing a damage layer, having a built-in ion milling device.
FIG. 12 is a cross sectional drawing schematically showing the structure of an FIB device disclosed in the above publication. The main elements of this FIB device are a liquid metal ion beam irradiation device (focused ion beam irradiation device) 200, a gas ion beam irradiation device 201, and a sample stage 202.
The liquid metal ion beam irradiation device 200 scans specified parts of the surface of the sample 203 mounted on the sample stage 202 using a sufficiently focused ion beam (FIB) drawn out from a liquid metal ion source. As the liquid metal ion source, there is a Ga ion source, for example. The gas ion beam irradiation device 201 uniformly irradiates a region including a section that has been processed with an ion beam drawn out from a gas ion source.
With the above described FIB device, first of all, the sample 203 is subjected to section processing with an FIB from the liquid metal ion beam irradiation device 200. At the time of this section processing, a damage layer is formed on the section. After section processing, a region containing the processed section is irradiated, and the damage layer on the section is removed by etching.
There is also damage to the section caused by the gas ion beam irradiation, but only to a small extent. The thickness of the damage layer in the case of the liquid metal ion source is 20-30 nm, while for the gas ion beam the thickness of the damage layer is only a few nm, which means that the damage layer does not present a problem in section observation using a TEM or SEM.
As described above, in the case of slicing processing using a FIB, since it is possible to have a damage layer on the processed section, there is a problem in that it is not possible to carry out favorable section observation using a TEM or SEM etc.
By removing the damage layer after section processing with the FIB using the gas ion beam, the above described problem is solved, but in this case, a problem arises with regard to re-attachment of secondary particles, as will be described in the following.
A process of forming a re-attachment layer on the section is shown in FIG. 13(a) to FIG. 13(c). As shown in FIG. 13(a), an Ar ion beam is irradiated in order to remove the damage layer 203 formed on the section. The irradiation range of the Ar ion beam includes an adjacent surface 204 adjoining the section. If the Ar ion beam is irradiated to the adjacent surface 204, then secondary particles are ejected from the adjacent surface 204, as shown in FIG. 13(b). Secondary particles ejected, from this adjacent surface 204 are attached to the section after the damage layer 203 has been removed, forming the re-attachment layer 206 as shown in FIG. 13(c). This re-attachment layer 206 also impedes favorable section observation using a TEM or SEM.
To solve the problem of re-attachment of secondary particles from the adjacent surface due to the Ar ion beam, Japanese Patent Laid-open No. Hei.4-116843 discloses setting the direction of the Ar ion beam so that the Ar ion beam does not irradiate the adjacent surface (this document discloses a bottom surface). However, in this case there is the following problem.
The adjacent surface may also be a surface other than the bottom surface. For example, in the case of a sample that has been subjected to section processing shown in FIG. 10(c), the adjacent surfaces include side walls (side walls formed by the FIB section processing) positioned at both ends of the section 202 in the longitudinal direction, as well as the bottom surface. There is also the above described ejection of secondary particles from these side walls. Since the Ar ion beam is a beam that can not be sufficiently focused, it is not possible to carry out setting so that the two side walls and bottom surface are not irradiated. Accordingly, even if the Ar ion beam direction is set so that the bottom surface is not irradiated, the Ar ion beam will inevitably irradiate the two side surfaces, and a re-attachment layer will be formed on the section.
In addition, in preventing the Ar ion beam from irradiating the bottom surface, the direction and positional relationship of the Ar ion beam with respect to the sample must be set with high precision, and this kind of setting takes time.
By making the region to be processed by the FIB sufficiently large with respect to the diameter of the argon ion beam, it is possible to make the argon ion beam irradiate only the region to be processed, but in this case the processing time using the FIB becomes longer.
The object of the present invention is to solve the above described problems, and to provide an ion beam device, and ion beam processing method, and a holder member, capable of suppressing re-attachment of secondary particles to the section in a straightforward manner.